1. Field of the Invention
The present invention relates to a cathode-ray tube for color picture tube, color monitor and the like, and more particularly, to a cathode-ray tube having a yoke mounting part in the form of a pyramid to raise a degree of freedom in rotation during an ITC process and enhanced productivity, with the radii of inner and outer curvatures of the funnel and the thickness being optimized to enhance atmospheric pressure resistance and deflection sensitivity.
2. Background of the Related Art
In general, a color cathode-ray tube, for example, has an outer vacuum tube made of glass that comprises a panel having an approximately rectangular screen, a funnel joined to the panel, and a cylindrical neck joined to the funnel. The neck is internally provided with electron guns emitting three electron beams, and a deflection yoke is provided around the circumference of the funnel to control deflection of the electron beams. A portion of the funnel in which the deflection yoke is mounted is referred to as xe2x80x9cyoke mounting partxe2x80x9d.
The above-structured cathode-ray tube has the electron guns arranged in a line for emitting three electron beams on the same horizontal plane and scans the electron beams over the whole screen in such a manner that the electron beams are deflected with a pincushion-shaped horizontal deflection magnetic field and a barrel-shaped vertical deflection magnetic field generated from the deflection yoke.
Such a general cathode-ray tube has the deflection yoke usually designed based on the funnel. However, in a pyramidal funnel and deflection yoke structure, the cone of the funnel, i.e., the yoke mounting part has to be designed to have an optimal inside profile as determined in consideration of the explosion characteristic and the beam strike neck (BSN) to the beam trajectory, the funnel being designed based on the deflection yoke in the order of deflection yoke profile modeling, beam trajectory calculation, vacuum stress calculation at the funnel bulb, and deflection yoke shape modeling considering deflection sensitivity. This constraint on designing the yoke mounting part requires optimization in designing the outside profile of the funnel so as to enhance atmospheric pressure resistance in consideration of deflection sensitivity and explosion characteristic in a situation that the values related to the inside profile of the funnel are almost fixed.
A color cathode-ray tube is illustrated in FIGS. 1 and 2 as an example of the above-constructed conventional cathode-ray tube.
The color cathode-ray tube has an outer vacuum tube 10 made of glass.
The outer vacuum tube 10 comprises a face panel 3 having an approximately rectangular effective part 1 and a skirt part 2 provided in the periphery of the effective part 1, a funnel 4 joined to the skirt part 2, and a cylindrical neck 7 extending from the funnel 4.
The effective part 1 of the face panel 3 has an approximately rectangular form with horizontal and vertical axes H and V perpendicular to each other through a tubular axis Z of the cathode-ray tube.
And, a deflection yoke 6 is externally provided over an area ranging from the neck 7 to the funnel 4. The funnel 4 has a small-diameter region, so-called yoke mounting part 12 extending from the joint with the neck 7 to the mount position of the deflection yoke 6., i.e., extending to the side of the face panel 3.
On the inner surface of the effective part 1 of the face panel 3 are provided a fluorescent screen S comprising three dot or stripe type fluorescent layers emitting blue, green and red lights, and a stripe type light-shielding layer interposed between the fluorescent layers.
The outer vacuum tube 10 is internally provided with a shadow mask 11 as a dichroic electrode opposite to the fluorescent screen 5.
And, electron guns 9 emitting three electron beams 8 are provided in the neck 7. The three electron beams 8 emitted from the electron guns 9 are deflected by the horizontal and vertical magnetic fields generated from the deflection yoke 6, thus horizontally and vertically scanning the fluorescent screen 5 via the shadow mask 11 to form a color image on the screen 5.
The yoke mounting part 12 of the funnel 4 in which the deflection yoke 6 is mounted in the color cathode-ray tube has an approximately pyramidal form. Here, the deflection yoke 6 is of a saddle shape with less leakage magnetic field and comprises a cylindrical frame made of a synthetic resin for fixing horizontal and vertical deflecting coils and a core. More specially, the pyramidal yoke mounting part 12 has a circular cross section perpendicular to the tubular axis Z as the neck 7 around the joint with the neck 7 and an approximately rectangular cross section in conformity with the profile of the effective part 1 of the face panel 3, as shown in FIGS. 3 and 4, around the central portion along the tubular axis Z and the end portion on the side of the fluorescent screen 5.
As illustrated in FIG. 4, the cross section of the yoke mounting part 12 has the outside profile in an approximately rectangular form constituted by the continuity of a pair of circular arcs 20 for a horizontal radius Roh having a center on the horizontal (major) axis H with respect to the effective part 1, a pair of circular arcs 21 for a vertical radius Rov having a center on the vertical (minor) axis V, and a pair of circular arcs 22 for a diagonal radius Rod having a center on the diagonal axis D.
That is, as shown in FIG. 3, the cross section of the yoke mounting part 12 has the inside profile with inner diameters La, Sa and da in the directions of horizontal (major), vertical (minor) and diagonal axes H, V and D, respectively, extending from the joint with the neck 7 to the end of the deflection yoke 6.
The yoke mounting part has, as also shown in FIG. 3, outer diameters DA, LA and SA in the directions of diagonal, horizontal (major) and vertical (minor) axes D, H and V, respectively, extending from the joint with the neck 7 to the screen side of the deflection yoke 6, i.e., the end of the deflection yoke 6.
As such, the cross section of the yoke mounting part 12 perpendicular to the tubular axis Z has the outside profile almost in the same circular form as the neck 7 around the joint with the neck 7, and in an approximately rectangular form on the side of the fluorescent screen 5 with a gradual decrease in the outer diameters LA and SA in the directions of the major and minor axes, respectively, with respect to the outer diameter DA in the direction of the diagonal axis D.
While on the other, the yoke mounting part 12 has the inside profile not in a perfect plane but in a pincushion form protruding in the direction of the tubular axis Z, as illustrated in FIG. 3. That is, the cross section perpendicular to the tubular axis Z of the yoke mounting part 12 has the inside profile not in a perfect rectangular form but in an imperfect rectangular form of which the sides form a convex curve protruding in the direction of the tubular axis Z.
Each short side 24 for the inside profile of the yoke mounting part 12 is in the form of a convex curve having an apical part on the horizontal axis H, each long side 25 being in the form of a convex curve having an apical part on the vertical axis V.
In a case where the long and short sides 25 and 24 for the inside profile are in the form of a convex curve, the individual corners are all formed with arc curves, i.e., arcs 22 and 26 in both inside and outside profiles so as to prevent an abrupt decrease in the diagonal thicknesses due to a difference between inner and outer diameters La and LA in the direction of the horizontal (major) axis, and a difference between inner and outer diameters Sa and SA in the direction of the minor axis.
The long and short sides perpendicular to the tubular axis Z with respect to the inside profile of the yoke mounting part 12 have thicknesses Th and Tv as determined based on the profile of an electron beam passage region 23 in the yoke mounting part 12, as shown in FIG. 5.
Therefore, as described above, the cross section of the yoke mounting part 12 has an inside profile formed with convex curves in the form of a pincushion approximate to the electron beam passage region 23, thereby converging the inside of the yoke mounting part 12 on the electron beam passage region 23.
The cross section of the yoke mounting part 12 of the funnel 4 has the outside profile in an approximately rectangular form, with the inside profile having the respective sides in the form of a convex curve protruding in the direction of the tubular axis Z. This approximates the inside of the yoke mounting part 12 to the electron beam passage region 23 and enhances deflection efficiency of the deflection yoke 6 to reduce deflection power consumption.
Such a pyramidal yoke mounting part 12 enables reduction of the horizontal and vertical diameters in the directions of the horizontal (major) and vertical (minor) axes H and V of the deflection yoke 6, respectively. Thus the horizontal and vertical deflecting coils of the deflection yoke 6 become closer to the electron beams 8 to efficiently deflect the electron beams 8 and reduce deflection power consumption.
However, in the yoke mounting part 12 having the outside profile in an approximately rectangular form constituted by the continuity of radii of curvatures Roh, Rov and Rod along the major, minor and diagonal axes perpendicular to the tubular axis Z, simply decreasing the diameter of the neck 7 or the outer diameters of the yoke mounting part 12 of the funnel 4 may have the electron beams 8 out of the line collide with the inner wall in the vicinity of the neck 7 of the funnel 4, thus forming a non-fluorescent region 27 on the fluorescent screen 5 at which the electron beams 8 do not arrive, as shown in FIG. 7. And, as the yoke mounting part 12 approximates a rectangular form, deformation occurs in originally flat vicinities 100 and 101 of the horizontal and vertical axes H and V in the directions as indicated by broken lines 103 of FIG. 7 clue to a load F of the atmospheric pressure. The deformation causes compressive stresses "sgr"H and "sgr"N on the outer surface of the horizontal and vertical vicinities 100 and 101 of the yoke mounting part 12 and an excessive tensile stress "sgr"D on the outer surface of a vicinity 102 of the diagonal axis D, as a result of which the outer vacuum tube 10 has a deterioration of the atmospheric pressure resistance and safety.
In an attempt to overcome the problem for wide-angle deflection, for example, a tube has been developed to have a deflection angle of 110 degrees. However; such a wide-angle deflection increases a deflection angle of the corners to cause neck shadow, i.e., beam strike neck (BSN) on the corners of the inner surface of the funnel and deteriorate atmospheric pressure resistance.
In the aspect of this problem,Japanese Patent Sho8-225545 andjapanese Patent Pyung 10-154472 disclose a yoke mounting part of the funnel 4 in the conical form that reduces the distance from the deflection yoke to the electron beams in order to prevent formation of the non-fluorescent region and deterioration of atmospheric pressure resistance.
According to Japanese Patent Sho58-225545, the inner surface of the conical funnel has appropriate grooves at the corners to prevent collision of electron beams with the inner surface of the funnel arid thereby enhance deflection sensitivity. Also, Japanese Patent Pyung10-154472 describes a yoke mounting part whose cross section has inside and outside profiles with two horizontal sides opposite to each other based on the horizontal axis interposed between them in the form of a straight line and two vertical sides opposite to each other based on the vertical axis between them in the form of a convex curve protruding in the direction of the tubular axis, thus enhancing atmospheric pressure resistance with a thickness difference between the long or short sides and the corners.
However, with an excessive difference in the thickness between the long or short sides and the corners in order to secure the margin of BSN, the conical cathode-ray tube according to Japanese Patent Sho58-225545 may have an increase in the maximum vacuum strength (tensile strength) on the corners of the funnel to cause explosion of an exhaust gas in the manufacture of the cathode-ray tube and increment the distance from the deflecting coils to the electron beam passage region,thus increasing deflection power consumption. Otherwise, when the thickness difference between the long or short sides and the corners is decreased in order to prevent explosion and reduce deflection power consumption, an excessive stress occurs on the BSN and the long and short sides.
According to Japanese Patent Pyung10-154472, the yoke mounting part has an inside profile in the form of an inwardly projecting pincushion to increase a thickness representing a difference between inner and outer diameters, which increases the weight of the funnel.
Especially, the wide-angle deflecting pyramidal cathode-ray tube has a difficulty in securing neck shadow and the margin for rotation of the deflection yoke in an ITC process (a step of controlling the deflection yoke to optimize the screen during installation of the deflection yoke after manufacture of a tube), thus resulting in deterioration of productivity.
It is, therefore, an object of the present invention to provide a cathode-ray tube that optimizes inner and outer curvatures and thicknesses of a deflection yoke mounting part of a funnel to secure the margin for ITC rotation and atmospheric pressure resistance and maximize deflection sensitivity, in which when divided into equal xe2x80x9cnxe2x80x9d parts, the yoke mounting part in the form of a pyramid has the inner and outer curvatures differentiated at the individual positions to minimize the thickness of the funnel.
In accordance with an aspect of the present invention to achieve the above object, there is provided a cathode-ray tube which has a panel provided with a fluorescent screen on an inner surface thereof, a funnel joined to the panel, a neck joined to the funnel and provided with electron guns facing the fluorescent screen, and a pyramidal yoke mounting part provided in a region extending from the neck side to the panel side. When the yoke mounting part has inside and outside profiles in an approximately rectangular form and the profiles include a position where the cross section of the yoke mounting part perpendicular to a tubular axis is maximized, other than major and minor axes, a curvature ratio on an inflection point with respect to the tubular axis is in the range of 0.85xe2x89xa6Rov/Rivxe2x89xa60.90 and 0.89xe2x89xa6Roh/Rihxe2x89xa60.93, wherein Rov and Riv are radii of outer and inner curvatures on the minor axis perpendicular to the tubular axis, respectively; and Roh and Rih are radii of outer and inner curvatures on the major axis perpendicular to the tubular axis, respectively.
Preferably, in the cross section of the yoke mounting part, the ratio of a radius of outer curvature to a radius of inner curvature on the minor axis perpendicular to the tubular axis is in the range from 0.70 to 0.90, and the ratio of a radius of outer curvature to a radius of inner curvature on the major axis is in the range from 0.70 to 093. If the ratio of a radius of outer curvature to a radius to inner curvature on the major or minor axis of the yoke mounting part is less than 0.70, the diagonal thickness of the funnel becomes larger to increase deflection power consumption, thereby deteriorating deflection sensitivity and causing neck shadow and a difficulty in the ITC process. If the ratio exceeds 0.90 or 0.93, the diagonal thickness of the funnel becomes smaller to deteriorate tensile strength. It is therefore desirable that the curvature ratio satisfies the above relation, in order to secure sufficient atmospheric pressure resistance, deflection sensitivity and the margin for ITC rotation.
In accordance with another aspect of the present invention, there is provided a cathode-ray tube which has a panel provided with a fluorescent screen on an inner surface thereof, a funnel joined to the panel, a neck joined to the funnel and provided with electron guns facing the fluorescent screen, and a pyramidal yoke mounting part provided in a region extending from the neck side to the panel side; and when the yoke mounting part has inside and outside profiles in an approximately rectangular form and the profiles include a position where the cross section of the yoke mounting part perpendicular to a tubular axis is maximized, other than major and minor axes, the ratio of a radius of outer curvature to a radius of inner curvature for long sides on the major axis perpendicular to the tubular axis being in the range from 0.70 to 0.93, the ratio of a radius of outer curvature to a radius of inner curvature for short sides on the minor axis being in the range from 0.70 to 0.90.
Optionally, when the yoke mounting part is equally divided into the vicinity of a joint with the neck and a deflection base point, (1) a curvature ratio in the vicinity of the joint with the neck is in the range of 0.70xe2x89xa6Rov/Rivxe2x89xa60.75 and 0.70xe2x89xa6Roh/Rihxe2x89xa60.75; and (2) a curvature ratio on the deflection base point is in the range of 0.75xe2x89xa6Rov/Rivxe2x89xa60.81 and 0.75xe2x89xa6Rob/Rihxe2x89xa60.77, wherein Rov and Riv are radii of outer and inner curvatures for the short sides perpendicular to the tubular axis of the yoke mounting part, respectively; and Roh and Rih are radii of outer and inner curvatures for the long sides perpendicular to the tubular axis, respectively.
Optionally, a curvature ratio on an inflection point with respect to the tubular axis is in the range of 0.85xe2x89xa6Rov/Rivxe2x89xa60.90 and 0.89xe2x89xa6Roh/Rihxe2x89xa60.93.
As such, the yoke mounting part has the ratio of a radius of outer curvature to a radius of inner curvature differentiated in the vicinity of the joint with the neck, on the inflection point and on the deflection baseline to minimize the thickness of the funnel, especially diagonal thickness, thus minimizing atmospheric pressure stress imposed on the funnel and enhancing the margin for ITC rotation and deflection sensitivity.
Thus the atmospheric pressure resistance of the wide-angle deflecting outer vacuum tube can be secured to effectively reduce deflection power consumption and thereby realize high brightness an high frequency deflection.